How to Clean Snowmobile Clutches

Snowmobile clutches have a difficult life. At the flip of a throttle lever, they go from idling to transmitting full power from the engine’s crankshaft to the chassis’ jackshaft. They must perform shifting duties under harsh conditions and rider styles from mild to wild.

Poorly maintained or worn out clutches can steal torque and horsepower from the powertrain. Issues often include misalignment of the clutches, worn bushings or rollers, or worn or incorrect drive belts. The basic flyweight-style drive clutch dates back to the early 1970s. The principles of operation apply to most any flyweight-style drive clutch used by Arctic, Polaris and Yamaha, plus the Comet series of clutches from the vintage 1972 model 100-C to the modern 108-EXPs.

STEP 1

STEP 2

Teardown: Disassembly of the driven clutch hasn’t changed significantly since the reverse cam secondary was invented by John Deere in 1976. Remove the three nuts holding the roller plate onto the movable half, taking care to hold against the spring preload before fully removing the retaining nuts.

STEP 3

STEP 4

Helix Removal: An Allen wrench is needed to remove the helix cam from the fixed half of the drive. The angle of the helix strongly influences the shifting action of the driven. A shallower angle allows for faster RPM building and backshifting, while a steeper angle enables a fast upshift but slower backshifting. A compound or multi-angle helix can tune around those characteristics for fast acceleration and a quick backshift.

STEP 5

STEP 6

Cleaning: The black residue shown is belt crud, and it was embedded on the face of the driven clutch. Sanding and wiping down with brake parts cleaner effectively removes it, restoring clutch traction with the drive belt. Some racers even sand the edges of their belt to remove any glazing.

STEP 7

New Helix: After a complete cleaning and inspection, this Cat roller driven was ready for a new billet helix. A multi-angle unit was selected to enhance performance for cross country racing, but many options are available for this particular driven clutch.

STEP 8

Reassembly: The original spring was reused for this application, preloaded one ramp with the roller end cap and the nuts torqued. The spring works with the helix to control shifting and to a lesser degree RPM. A stiff spring will provide more resistance to upshifting, allowing RPMs to build and provide a quicker backshift. This clutch has several holes to allow for some preload adjustment and fine tuning of spring tension. Of course, a range of springs are also available.

That’s it for the driven clutch! Easy, right? Step-by-step care instructions for the drive clutch are slightly more complicated. See the gallery below.

Like the driven (secondary) clutch, the drive clutch (also called the primary) needs a thorough inspection prior to the season. There are a few more parts, so follow closely.

STEP 1

Removal: No matter what brand clutch you have, it’s best to have the proper pullers to install and remove the drive clutch. Note that some brands’ pullers or holders can damage other brands clutches, while some pullers directly interchange. Use a proper holder to allow the retaining bolt to be removed or installed, and then make sure to put a dab of grease on the end of the puller bolt and threads to ease use. Thread in the puller bolt until the drive “pops” loose from the crankshaft taper.
NOTE: A proper drive clutch puller designed for your make and model clutch is required to “pop” the drive off the tapered end of the engine crankshaft. Many clutch pullers and holding tools are not interchangeable between style or brand. Using improper tools may actually cause damage.

STEP 2

Cover Removal: We like to pull one bolt from each tower before removing the final three. Remember, the cover is spring-loaded, so work slowly and hold down on the cover while loosening the last three bolts.

STEP 3

Cover Off: With the cover removed, the drive spring is released. The spring’s main job is to hold the clutch sheaves open at idle to engagement RPM. The spring also primarily sets what RPM the clutch starts to engage. The stiffer the spring, the higher the engagement RPM.

STEP 4

STEP 5

Flyweights: This Cat drive uses three flyweight and retaining hardware sets. The mass and shape of the weight determine the shift pattern and max engine RPM. Generally speaking, a heavier weight reduces a given engine’s RPM while a lighter weight increases it.

STEP 6

Cleaning: After a good cleaning and inspection of the movable face bushings, the belt sheaves were sanded with 400-grit wet/dry paper and cleaned with brake parts cleaner. If your bushings don’t check out, some may be available from the manufacturer, but some may have to use aftermarket kits. These checked out fine. Had they not, the spider would have been removed to gain access to the moveable face and spider bushings.

STEP 7

STEP 8

Weight Reinstallation: It’s easiest to slide the flyweights into position horizontally, while pinching the flat washers on each side of the weight and dropping the retaining bolt into position. Do not over-torque the lock nut, as it can distort the towers, pinching them on the spider.

STEP 9

Spring Reinstallation: Sometimes simple tools come in handy, like using blocks of wood to hold the drive clutch open when reinstalling the drive spring and cover plate. The original black/blue drive spring was retained as it gave the desirable 5,000 rpm engagement speed, while the flyweights were lightened up to increase the max RPM.

STEP 10

Cover Install: With blocks holding the clutch open, check for alignment features on the over plate to moveable face. Push down firmly on the cover plate to compress the spring and thread in on the bolt at each location with your free hand. If you service clutches often, you can find nicer tools for holding them.

STEP 11

Tightening the Cover: The cordless impact makes short work of tightening the six cover bolts, completing the clutch job. Make sure to run them down evenly before the final torque to prevent the cover from binding on the center post. I find it handy to note the spring, weight and date on the cover with a sharpie.

More clutch calibration basics
For calibration, a lighter flyweight allows for less belt pressure at a given RPM, allowing higher engine RPMs, while a heavier weight will reduce max RPMs with increased belt pressure. How the mass is distributed on the weight can also change the operational characteristics. For example, mass along the tip will have far more influence than mass around the mounting hole. The shape of the weight can also influence the engagement RPM. Features such as a flat or a notch for the roller to sit in at idle increase the engagement RPM above what the spring would do alone with a smoother ramp profile.

The secondary clutch is a load-sensing unit that primarily controls shift-out and backshifts. Also, it influences top engine RPM and load. The secondary helix was introduced in the late 1960s and was quickly adapted across the industry. The now-common reverse helix design was brought to the world by John Deere for the 1976 model year. Roller driven clutches, introduced by Aaen Performance in the early ’90s and then popularized by Arctic Cat in the mid ’90s, might be something we take for granted now. But at the time, a driven clutch that backshifted (or downshifted quickly) was a significant upgrade in state-of-the-art clutching.

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